The present invention is directed to windmills and, in particular, to means for controlling turbine-blade pitch.
Cost and efficiency considerations dictate that windmill parts should be as light in weight as possible. On the other hand, the need to withstand wind stresses requires that the windmill parts be relatively massive. In order to reduce mass, therefore, windmills have been designed to minimize the stress experienced by the structure in response to expected wind force.
One way to reduce blade stress is to incline the blades slightly forward along the axis of rotation, i.e. in the wind direction. The centrifugal force experienced by the blades during turbine spin thus partly counteracts the wind force, which tends to bend the blades in the forward direction. This expedient, however, depends on a proper orientation of the windmill with respect to the wind direction. Specifically, this stress reduction provided by inclination of the blades depends on the degree to which the axis of rotation is aligned with the wind direction.
Although the windmill turbine is free to rotate to align itself with the wind, I have found that windmill turbines do not always respond quickly enough to sudden wind changes to maintain the desired alignment, and excessive blade stress can therefore result. Under such stress, blades may be damaged at their roots, or their tips may be bent back (downwind) and strike the tower.
It is an object of the present invention to reduce the likelihood that sudden wind shifts will enable the wind to apply a force to the blades in such a direction that the centrifugal force does not counteract the wind force.